Bending strength of cast iron circular plates were examined using specimens of various strength, diameter and thickness. Cast iron disks did not fracture at the maximum load, but still supported the load with increasing deflexion. Conventional bending strength σ_bp defined by an elastic formula and the maximum load had good correlation with the tensile strength σ_t. It depended on the thickness of the disk h, but just slightly on diameter D. Thus the following equation was valid experimentally.
    σ_bp=2σ_t+7+100/h (kg/mm²)
The strength of the disk is estimated by
    P_m=σ_bp⋅h²/[3/2π+(1+ν)(0.485C ln (D/2h)+0.52)]
The calculated values well agreed with the experimental values for lathed specimens of σ_t=15∼35kg/mm², h=5∼20mm, D=200∼400mm. The formula was also valid for as cast disks in the region of σ_t<25kg/mm² where σ_t is not the strength of the standard test piece, but is that of the casting.

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  In ferritizing annealing, the ferrite grain size is refined and the toughness is increased when it is below the A₁ temperature after normalizing. On the other hand, in annealing below the A₁ temperature after quenching from the austenite range the transition temperature by precipitation of secondary graphite and refining of the ferrite grain size tends to become low, but energy absorption in the upper shelf range of the transition curve is reduced. The martensite matrix of nodular cast iron is not good in terms of toughness because the carbon content is apt to become very high. It is found, on the other hand, that the bainite matrix has good toughness and strength.

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  The differences in the characteristic of cast iron melt according to the types of melting furnaces, such as cupola and low frequency induction furnace, may be mainly due to the difference in melting speed. The authors conducted model experiments by melting at rapid and slow heating speeds with various maximum superheat temperatures. In rapid melting, graphite nucleation became gradually inactive as superheat temperature rose. In slow melting, especially, irons superheated to higher than 1,500°C, showed a rapid increase in chill depth which indicates a harder nucleation of graphite. The cause of these phenomena is ascribed to the difference in the quantity of carbon microsegregation in the melt. Thus a low carbon steel rod was dipped in the melt under a constant condition, and the rate of carbon diffusion was examined. In slow heating and high superheat melting, the rod diameter decreased rapidly. This signified higher effective carbon concentration in the melt. On the other hand, rapid heated and low superheated melt was considered to be a colloidal liquid containing carbon microsegregation as a dispersed phase. This carbon microsegregation may effectively act on graphite nucleation in eutectic solidification.

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  A number of semi-solidus temperature of Al-Cu and Al-Si alloys were determined employing two experimental methods, namely by measuring the starting temperature of contraction and the critical temperature below which the cast material acquires strength. A slight difference was found between values of these two methods, the latter method having a tendency to show lower semi-solidus. It is thus suggested that the liquid-solid zone in phase diagram is divided into three zones by the following criteria. (1) Seme-liquid zone. (2) Primary semi-solid zone : range between semi-solidus determined by the contraction measurement and strength measurements. In this range, the material is characterized by low strength and high elongation. (3) Secondary semi-solid zone : range between semi-solidus determined by the strength measurement and solidus. In this range, the material shows medium strength and low elongation.

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  It has been known that solid skin moves toward a mold or a metal when cast iron is solidified in the sand mold. Movement of the solid skin is affected by its own strength. However, the strength of the solid skin has not been known. In this study, the strength of the solid skin and its movement during freezing in the mold were measured when molten cast iron was poured into an N-process mold.
  The strength of the solid skin is low immediately after pouring, but increases rapidly after a certain period of time. The strength of the solid skin immediately after pouring was decreasing in the order of magnesium treated spheroidal graphite iron, calcium treated spheroidal graphite iron, inoculated gray iron and non-inoculated gray iron. Carbon content has little effect on the strength of the solid skin. The solid skin moved toward the metal immediately after pouring, but it moved toward the mold after a certain period of time. The length of mevement toward the mold increased as the strength of the solid skin decreased.

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  The morphological change of graphite in gray cast iron during solidification when the melt was alloyed with pure tellurium was studied by using scanning electron microscope. It seemed that the adsorption of tellurium on the prism plane of graphite crystal suppressed the crystal growth on the plane so that it accelerated the growth of graphite crystal on c-plane in c-axis direction. Subsequently, a hexagonal stacked structure of graphite crystal is observed on a deep etched alloy having higher content of tellurium when slow cooling but is not so remarkable in fast cooling. The same results on morphological change of graphite during solidification are obtained both in nickel-carbon hypereutectic alloy and iron-carbon-silicon hypereutectic alloy. Moreover, it can be assumed that in eutectic reaction of hypoeutectic iron, there is some suppression of crystal growth of graphite in the c-axis direction by the cooperative growth of γ-dendrite by tellurium addition which causes the supercooling of the melt and leads to the eutectic reaction in the meta-stable system.

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